1. Field of the Invention
The present invention relates to a magnetic memory device for magnetically memorizing information by the use of magnetic domains generated in a magnetic medium having an easy axis of magnetization orthogonal to a principal surface thereof and, in particular, to a so called Bloch line memory device using vertical Bloch-lines (VBLs) in stripe-domain walls as logic units of information.
2. Description of the Prior Art
As a magnetic memory device using the magnetic domains, a magnetic bubble memory device has been well known in the prior art wherein magnetic bubbles, namely, cylindrical domains are used as magnetic domains and transferred along predetermined propagation patterns by application of magnetic field.
Recently, the Bloch-line memory device has been proposed by Konishi and Hidaka as disclosed in EP-A-0106358 (which is corresponding to copending U.S. application Ser. No. 542,963 filed on Oct. 18, 1983 and now U.S. Pat. No. 4,583,200 by Konishi and Hidaka and assigned to the same assignee of the present application).
The Bloch-line memory device enables one to provide a memory device having an extremely high memory density in comparison with the conventional magnetic bubble memory device.
As disclosed in EP-A-0106358, the Bloch-line memory device comprises a magnetic medium, such as a garnet film, having an easy axis of magnetization orthogonal to a principal surface thereof. In the magnetic medium surface, at least one magnetic domain is generated in a stripe shape having opposite ends. The stripe-domain is surrounded by a domain wall laid in parallel with the easy axis of magnetization. The domain wall has wall magnetization along the domain wall. An information signal is written into the domain wall at one end portion of the stripe-domain in a form of a pair of vertical Bloch lines. The VBL pair is detected at the other end to produce a read-out signal. In order to propagate or transfer the VBL pair from the write-in end to the read-out end, pulsed magnetic field is applied to the magnetic film.
The reliable step-by-step propagation of the VBL by application of the pulsed magnetic field requires an improvement of the stripe-domain stabilization.